Uber has already outgrown its brand new offices

Uber employees work away from their desks at their new office in San Francisco, Calif. on Friday, May 30, 2014. (James Tensuan, The Chronicle)

Uber is growing at a rapid clip — so rapid that it has already outgrown the splashy new Market Street headquarters the company moved in to in May.

Developer Alexandria Real Estate Equities announced on Thursday that it has struck a deal to develop a new 423,000-square-foot space in Mission Bay for the ride-hailing app — effectively tripling Uber’s San Francisco footprint.

The move is Uber’s eighth since its founding in 2009. Alexandria CEO Joel Marcus said that Uber’s new space will include two 10-story buildings with a “high-tech, urban campus feel.”

Uber signed a 15-year lease on two properties at 1455 and 1515 Third Street. The space will have room for at least 2,000 employees. Uber will own 49 percent of the development in a joint venture with Alexandria.

Uber, which is now valued at more than $18 billion and aggressively expanding across the globe, moved in to an 88,000-square-foot space at 1455 Market St. four months ago. That space has room for 600 people, and the company has leased an additional 132,000 square feet in the same building, but has not yet moved in.

Uber will keep those Mid-Market offices, but move its headquarters to Mission Bay.

Marcus said construction will start in January and be completed by the end of 2016. The complex will be near the planned Golden State Warriors arena, on land previously purchased from Alexandria by Salesforce.com. Salesforce bought a total of 14 acres in the area for nearly $250 million in late 2010 to build an offices campus, but dropped the plan two years later and instead decided to expand into the Financial District, leasing half of what is expected slated to be the tallest building in San Francisco.

Alexandria bought back the two parcels that Uber will lease on Third Street for $125 million, including plans, permits and parking space.

The parcels have already been approved for offices space under Proposition M, a 1985 law designed to prevent excessive office development by limiting the amount of office space the city can approve each year.

Marcus said that Uber’s new space will mirror the aesthetics of its present Mid-Market headquarters, with an open office plan, lots of meeting space and waterfront views.

Mission Bay was envisioned as a biotech hub, but Marcus said more and more consumer tech companies are looking at expressing interest in the area.

“These kinds of companies express more and more interest in building campuses in San Francisco’s urban core,” he said.